Add config files for supported machines

[xylar]

Fix netcdf-fortran version to match conda-forge pin

Fix how machine configs from mache and polaris are read during bootstrapping.

Checklist

• [x] Testing comment in the PR documents testing used to verify the changes

[xylar]

Testing

I ran:

./configure_polaris_envs.py --conda ~/mambaforge/ --env_name polaris_test --recreate --verbose

on my linux laptop and it produced the expected load_polaris_test_mpich.sh activation script.

I ran:

./configure_polaris_envs.py --env_name polaris_test --conda ~/chrysalis/mambaforge/ --verbose

on Chrysalis and it took its sweet time but I eventually got the expected load_polaris_test_chrysalis_intel_openmpi.sh activation script.